The present invention relates in general to police radar detectors and, more particularly, to police radar detectors and methods of operating police radar detectors wherein an improved frequency scheme enables improved sweeping of the X, K, K.sub.u, and K.sub.a radar bands, and also selective sideband suppression during sweeps of the X, K and K.sub.a radar bands.
Police have used radar waves to monitor the speed of motor vehicles for many years. The frequencies currently used throughout the world include: the X band--10.50 gigahertz (Ghz) to 10.55 Ghz; the K.sub.u band--13.40 to 13.50 Ghz; the K band--24.05 Ghz to 24.25 Ghz; and the K.sub.a band--33.40 Ghz to 36.00 Ghz. To alert motorists of the presence of police radar, electromagnetic signals within these radar bands are monitored using a police radar detector which issues an audible and/or visual alert upon detection of a radar signal within one of the bands.
Police radar detectors are basically superheterodyne radio receivers in which the tuning of the receivers is repeatedly swept through the frequencies which are to be received or detected, i.e., the frequencies of the radar bands. A typical superheterodyne radio receiver includes an antenna for receiving electromagnetic signals and a circuit for mixing signals from the antenna and local oscillator (LO) signals to convert the frequency of received electromagnetic signals to the frequency of an intermediate frequency (IF) with the LO being swept in frequency to tune the required frequencies. Incoming electromagnetic signals can then be received at the LO frequency plus or minus the IF frequency, known as upper and lower sidebands, respectively.
Generally, signal reception occurs in only one of these two sidebands and the other sideband or image frequency is suppressed by filtering or phasing to thereby perform single sideband (SSB) reception. SSB operation is usually preferable because it generally delivers improved noise figure relative to double sideband (DSB) operation and also reduces sensitivity in the alternate sideband, thus reducing susceptibility to undesired signals. Sometimes DSB operation is intentionally adopted in the interest of economy or because in some circumstances it can facilitate expanded frequency coverage.
The frequencies used within the police radar detector, including frequencies or swept frequency bands of local oscillators and frequencies of intermediate amplifiers, and the tuning methods, are referred to in the art as frequency schemes and a variety of frequency schemes are known and utilized in police radar detectors. For example, see U.S. Pat. No. 5,068,663; 5,268,689; 5,305,007; and, 5,917,441.
While known frequency schemes are satisfactory for operation of police radar detectors, there is an ongoing need for new and advantageous frequency schemes which improve operation of police radar detectors, reduce costs of manufacturing police radar detectors and/or simplify circuitry or operation of police radar detectors.